KHACHATRYAN, Ishkhan. On Some Formulas for the Index of a Linear Bounded Operator. Armenian Journal of Mathematics, Yerevan, Armenia, v. 2, n. 3, p. 94–101, 2009. Disponível em: https://armjmath.sci.am/index.php/ajm/article/view/57. Acesso em: 3 apr. 2025.